This invention relates to flameless atomic absorption spectroscopy, and more particularly to a new and improved graphite tube for use in measuring the flameless atomic absorption.
In flameless atomic absorption spectroscopy, the path of the rays of a photometer is directed through the longitudinal bore of a small graphite tube. The sample to be analyzed is introduced into this graphite tube, and the tube is then heated to high temperature by passing an electrical current therethrough. The sample is dried, ashed and eventually atomized so that a cloud of atoms is generated within the graphite tube, and the absorption of the cloud is then measured. During this procedure the graphite tube is maintained within an atmosphere of inert gas.
It will be appreciated that it is desirable to measure the temperature of the graphite tube during the aforesaid procedure. Such a measurement can be effected by pyrometric means, i.e. by measurement of the radiation emitted by the graphite tube. However, this involves the problem that in conventional graphite tubes, the emissivity of the surface and thus the radiation emitted at a certain temperature of the graphite tube is not constant, but varies during the course of use. That is, the emissivity of the graphite tube surface and thus the emission is initially relatively low, but during the course of repeated operations it increases until it finally reaches its final value. As a consequence the pyrometer is not able to give reliable and accurate measurements with any given graphite tube, and the accuracy is still worse for different or replacement tubes.
It is known to measure the temperature of workpieces in inductive heating devices by means of optical pyrometers, wherein the workpieces, prior to their insertion into the heating device, are painted at their measuring areas. This paint is so selected as to retain its characteristics unchanged under the influence of heat, as described in German Specification No. 1 145 383. However, such a paint can not be used at the temperatures required for atomic absorption spectroscopy and, furthermore, the vaporizing components of this paint would disturb the absorption measurement.